Micro-electromechanical systems (MEMS) piezoresistive transducers (PRTs) are well known and comprise a thin, silicon diaphragm supported over a pressure port by a pedestal. The pressure port is typically formed through a plastic housing, which can be attached to a source of a pressurized fluid, which can of course be liquid or gas. The pedestal that supports the diaphragm is typically attached to the housing by adhesive.
The diaphragm in which the piezoresistors are formed is supposed to deflect responsive to changes in the pressure of an applied fluid. Diaphragm deflection causes the size and shape of the piezoresistors to change, which causes their electrical resistance to change. The deflection of the diaphragm can thus be used to transduce or change a pressure into a measurable voltage change.
Plastic, adhesive, glass and silicon have different coefficients of thermal expansion. A well-known problem with mounting a thin diaphragm of single crystalline silicon, to a pedestal made of glass or silicon, which is also mounted to a plastic housing through adhesive, is the creation of thermally-induced stresses due to the different coefficients of thermal expansion. Thermally-induced stress will distort the shape of a diaphragm and distort the value of a measured pressure.
Those of ordinary skill in the art of MEMS PRTs know that the shape of a MEMS PRT is preferably a rectangular parallelepiped with the diaphragm being offset or located toward one side of the device or another. A problem with rectangular parallelepiped-shaped dies and pedestals that support the dies arises when the diaphragm is offset because offsetting the diaphragm tends to create uneven thermally-induced stresses in the die.
Uneven thermal stresses can be avoided by using a die and pedestal that is round or square, however, dies and pedestals that are square waste valuable space in a semiconductor wafer. Circular-shaped dies and pedestals are inefficient to fabricate. An apparatus for reducing thermally-induced electrical signals or noise would be an improvement over the prior art.